2010 BGD Practical 3 - Week 3 Summary
This page is a overview of events that occur in human development up to week 3 post-fertilization. From this Practical understand concepts of: fertilization, blastocyst development, implantation, bilaminar and trilaminar embryo formation, development of embryonic cavities and brief understanding of early placenta development. Note that this Practical has discussed mainly development of the embryo as placental development will be covered in detail in another practical (Practical 8 - Placenta and Fetal Membranes) The next Practical will continue on through embryonic development (Practical 6 - Implantation to 8 Weeks).
By the end of week 3 segmentation of the 3 germ layers has begun:
Ectoderm - central neural plate and lateral parts form epidermis
Mesoderm - midline notochord, adjacent somites, formation of the internal embryonic space (intraembryonic ceolom)
Endoderm - epidermal lining of gastrointestinal tract
|File:Stage8sem.jpg||== Carnegie Stages 8 ==
Features: brain fold, neural groove, amniotic sac, presomitic mesoderm, embryonic disc, primitive node, primative streak, primative groove, connecting stalk
Facts: Week 3, 17 - 19 days, 1.0 - 1.5 mm
View: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side. Amniotic membrane removed, brain fold top and connecting stalk bottom.
Events: Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.
Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.
From the primitive node a tube extends under the ectoderm in the opposite direction to the primitive streak. This tube forms first the axial process then notochordal process, then finally the notochord.
The notochord is a key to embryonic folding and regulation of ectoderm and mesoderm differentiation. It lies in the rostrocordal axis and the embryonic disc will fold either side ventrally, pinching off a portion of the yolk sac to form the lining of the gastrointestinal tract.
|File:4-5somiteSt10d21dorsaln4.jpg||== Carnegie Stages 9 ==
Features: embryonic disc, primitive node, primative streak, primative groove, somites, neural groove, brain plate region, connecting stalk, cut edge of amnion
Facts: Week 3, 19 - 21 days, 1.5 - 2.5 mm, Somite Number 1 - 3
View 1: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.
[#9labelled Stage 9 Labelled] | [#7molecular Stage 9 Molecular] | [Stage10.htm Stage 10]
Events: Ectoderm - Neural plate brain region continues to expand, neural plate begins folding over the notochord. Mesoderm - segmentation of paraxial mesoderm begins (1 - 3 somite pairs), cardiac primordium forms
Identify: neural groove and neural folds
Human Development Timeline
The table below shows human development features and approximate timing during the menstrual cycle to fertilization and the first 3 weeks of development.
The timing assumes fertilization the day after ovulation and the "weeks" refer to embryonic development and differ from clinical weeks (shown in brackets, from last menstrual period) and "stages" refer to Carnegie stages of development.
The pull down menus below will take you to specific features and the small images are linked to pages with more specific information (MH - background inormation and not part of this current Practical)
(Clinical Week 1)
|Menstrual Phase||File:Mcycle.GIFMenstrual cycle changes: Uterine endometrium (loss), Ovary (Follicle Development)|
|Proliferative Phase||File:Eprosm.gif File:Ovary20sm.jpgMenstrual cycle changes: Uterine endometrium (proliferation), Ovary (Follicle Development)|
(Clinical Week 2)
|File:Mprosm.gif File:Ovary5sm.jpgMid proliferative|
|File:Lprosm.gif File:Ovary10sm.jpgLate Proliferative|
|Ovulation||File:Follicle.jpg File:Ovulation2sm.jpg[../../Notes/week1.htm ]File:1egghum.jpg|
(Clinical Week 3)
|Secretory PhaseStage 1||File:2cell.gif File:1 2nuclei.jpg File:Secrsm.gif File:Husecsm.gifFertilization, Secretory Phase|
|Stage 2||File:CST2.gif File:Annemb.gif File:5 2cell.jpg File:Week1-poster.jpgMorula, Blastula|
|Stage 3||Blastocyst Hatching (zona pellucida lost)|
Blastocyst (free floating)
(Clinical Week 4)
(Clinical Week 5)
|Stage 7||File:CST7A.gif File:CST7B.gif|
|Stage 8||File:CST8.gif[Stage8sem.htm ]|
|Stage 9||File:CST9A.gif File:CST9B.gif|
Finished Lab 3 !
If you have finished and would like to apply your knowledge, I have also included some [BGDlabfertilization12.htm Clinical Questions] based around this period of development.
If you have finished and need some more help understanding this period of development, I have included some links to [BGDlabfertilization14.htm Online References].
If you have finished and are interested in looking at tissues involved in this period of development, I have included some links to [BGDlabfertilization13.htm Histology Images]. File:Rabbit.gif
|B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers|
- bilaminar- having 2 layers
- blastocyst- the developmental stage following morula, as this stage matures, the zona pellucia is lost allowing the conceptus to adplant and then implant into the uterine wall.
- blastomeres-the cells resulting from the initial rounds of mitotic division of the zygote. These cells become smaller (in cytoplasmic volume) with each division.
- corona radiata- Layer of follicle cells of cumulus oophorus remaining attached to zona pellucida of oocyte after ovulation.
- inner cell mass- the clump of cells found inside the blastocyst. These cells will go in to form the embryo, these are the "stem cells" (we here about in the media) that are totipotential, they can form any tissue in the embryo. Mature oocyte-the female germ cell released at ovulation from the ovary.
- morula &endash;(L. morus = mulberry) early stage of development (12-15 cells) Followed by formation of a cavity in the mass (blastocyst stage). (More? Week 1 Notes)
- parental genomes- the male (sperm) and female (oocyte) DNA which contributes to the embryo's cells.
- polar bodies- 3 exclusion bodies which contain the DNA not used by the embryo. Contributed to initially by the meiotic division of the oocyte.
- pronuclei- the male (sperm) and female (oocyte) nuclei within the fertilized oocyte, prior to their combination to form the new embryo's nuclei.
- trilaminar embryonic disc- the 3 layered embryo stage.
- Trophoblasts- (Gr. trophe = nutrition) outer layer of cells on blastocyst that will generate the embryonic part of the placenta.
- zona pellucida- glycoprotein shell that surrounds the oocyte through to blastula stage of development.
- Zygote- The first cell stage following fertilization of the oocyte by the sperm. This is the first cell of the conceptus which will divide into blastomeres.
[../wwwhuman/MCycle/MCycle.htm Human Menstrual Cycle]
[../Notes/week1.htm Week 1 Development]
[../Notes/week2.htm Week 2 Development]